We propose to study the specificity, function and control of T-helper cells which recognize idiotypes produced by B-cells. Selected myeloma and hybridoma anti-PC antibodies will be used as carriers in a TNP-specific B-cell response. T-helper cells recognizing the idiotypes of these PC binding antibodies are generated by priming with: a) PC binding idiotypes, b) low doses of anti-idiotypic antibodies or c) with PC-hemocyanin. Limiting numbers of T-cells are transferred to athymic syngeneic recipients and fragment cultures are prepared from the recipient spleens. The cultures are immunized with TNP-coupled anti-PC idiotypes and the production of anti-TNP antibodies is measured by ELIAS or RIA. Since the idiotype recognizing T helper cells are generated indirectly by anti-idiotype priming or by antigen exposure, the cellular circuits in the induction of T help will be studied. The role of T suppressor cells and antibodies will be investigated by adoptive transfers. Next, the fine specificity of idiotype recognizing helper T cells will be determined by in vitro inhibition of idiotype recognition using idiotype variants, anti-idiotype antibodies and isolated H and L chains. Single idiotope recognizing T helpers will be generated by monoclonal anti-idiotypic antibodies and their fine specificity will be analyzed using T15 variant hybridomas as TNP-antigens. Although the anti-TNP readout does not exactly mimic events which occur after exposure to antigen, this approach permits us to study idiotype-specific T-B interactions. Preliminary findings indicate that T helper cells recognize shared determinants on the T15 idiotype which are related to the site for PC. Since these target idiotopes are shared among serologically different idiotypes and appear to be stable during evolution they might function as specialized "Regulatory Idiotopes" in the control of the anti-PC response. Of particular interest is the long-term observation of possible changes in the specificity of T cells in aging, primed mice. Finally, attempts will be made to obtain T helper cell clones and to use their factors to study possible restriction in T-B interactions.